Pressure measuring devices, such as sphygmomanometers, include a pneumatic bulb which inflates a pressure chamber of an attached sleeve that is fitted over the arm or a leg of a patient. A diaphragm or bellows assembly, responsive to changes in fluid pressure of the pneumatic bulb and the sleeve pressure chamber is positioned in a dial indicator housing. The pointer of a dial indicator is interconnected to the bellows assembly by a movement mechanism, whereby inflation of the bellows causes corresponding circumferential movement of the pointer.
Typically, the above referred to movement mechanisms are quite intricate and complex, and are akin in terms of their manufacture and precision to Swiss watches. For example, in one such movement mechanism, a pair of diaphragm springs are attached adjacent opposing ends of a spindle. A bottom end of the spindle is placed in contact with the bellows assembly and a twisted bronze band perpendicularly disposed at the top end of the spindle is connected in parallel by a horizontally disposed bent spring part. As the spindle deflects axially in response to the inflation of the bellows, the bent spring part is also caused to deflect, thereby causing the band to twist. The pointer, attached to the bronze band, therefore is caused to rotate in relation to an adjacent dial face.
These devices include a plurality of moving components, each having multiple bearing surfaces. Therefore, such known assemblies must be manufactured with high degrees of tolerancing (and associated costs) in order to minimize errors.
In addition, any adjustments required after assembly of such mechanisms, such as to null the pointer or adjust the sensitivity of the device, require substantial teardown or at least significant and undesired disassembly of the measuring device.
Furthermore, separate support plates are required for independently supporting the movement mechanism and the bellows assembly, respectively, and for defining an expansion chamber for the bellows therebetween. Housings incorporating the same have compromised the ability to make a compact design.
A more recent and simplified movement mechanism developed by Applicants includes a vertically disposed axial cartridge including a spirally wrapped ribbon spring having one end mounted to an axially movable elongate pin and the remaining end to a fixed portion of the cartridge. A bottom portion of the pin is positioned relative to the expandable bellows, wherein subsequent axial translation of the pin elongates the spirally wound ribbon spring and produces repeatable circumferential movement of a pointer supported at the top end of the pin.
Subsequently, and in order to further reduce the overall size and complexity of the above structure, it has been determined that the diaphragm could be conveniently mounted and sealed relative to the bottom facing side of a single supporting plate, therefore making the design of a housing retaining the movement mechanism more compact. However, even with the improved design, there is still a continuing need in the field to provide an even more compact and streamlined housing. There is also a preexisting need to even further reduce the level of complexity in the manufacture of pressure measuring devices without compromising the reliability thereof.